Inorganic particles are a problem during oil/water separation of petroleum crude. The solids partially accumulate at the interface and may fill separation and storage tanks. In this paper anionic and nonionic surfactants are used to help remove the solids at the interface by water wetting the surface of the solids, and allowing them to settle to the bottom of the container. Careful observation during bottle testing was used to formulate a blend of demulsifier, anionic surfactant and nonionic surfactant, which facilitated the separation of the solids from the interface without increasing the water content of the emulsion right above the interface.
Petroleum crude usually is a mixture of oil, water and gas. The water is usually emulsified (dispersed) in the oil phase.(1) The water in oil emulsion is stabilized by emulsifiers naturally present in the crude, such as asphaltenes and resins,(2) and inorganic solids, such as sand, clay and iron sulfide.(3).
The separation of these phases, in particular of the water and oil, plays an important role on the quality of the final oil. The separation of these phases is normallyconducted in separation vessels. Heat and alternating current are used to accelerate the coalescence of water droplets. However, demulsiers are normally used to make the separation process more efficient. Demulsifiers are varied (ethoxylated/propoxylated copolymers of phenolic resins, polyglycol esters, diepoxides of polyglycols, etc).
Sometimes large amounts of inorganic solids are present. These solids may accumulate at the oil/water interface in the separation vessels, reducing the efficiency of the water separation process. Moreover, during normal oil/water separation operations these solids may partially fill separation and storage tanks.
It then becomes necessary to control the amount of solids at the interface for an efficient oil/water separation process. In most cases it is preferable to water wet these solids. These water-wet solids can fall to the bottom of the separation vessels for disposal. Water wetting of these solids is best accomplished by the selection of surfactants that are blended with the field injected demulsifier. Selection of effective surfactants for water wetting is often overlooked while bottle testing. During bottle testing of the emulsion these surfactants are chosen. The performance of the surfactant is judged by visual observation of solids in the water phase during bottle testing.
In this paper a typical Lloydminster crude emulsion was bottle tested. During this bottle testing, the surfactants and demulsifiers were blended to give a product that is both an efficient demulsifier and a solids control chemical.
During this work a typical bottle test procedure was used. Below is a concise description of the procedure. 1. A 160 mL prescription bottle was filled to the 100 mL mark with crude emulsion.
2. The crude emulsion was dosed with various concentrations of demulsifiers and surfactants.
3. The bottles were heated to 85 °C in a water bath for 1 hr.
4. The bottles were shaken in a shaking machine for 5 min at a rate of 120 shakes/min.
